Parameterize AccountData (#409)

* Add custom config example

* Make account data storage item configurable

* Fix contracts

* Regenerate polkadot codegen

* Fmt

* Specify different type for `MyConfig::Index`

* Update comment in custom config example

* Assign concrete types for default AccountData impl

* Fmt

* Fix contracts tests

* Fmt

* Add comments

* Unlink doc comment trait (subxt not in scope)

* Fix missing nonce field error message

* Update codegen/src/api/mod.rs

Co-authored-by: David <dvdplm@gmail.com>

* Update examples/custom_config.rs

Co-authored-by: David <dvdplm@gmail.com>

* Rename Nonce assoc type to Index for consistency

* Add module level docs about codegen assumptions

Co-authored-by: David <dvdplm@gmail.com>

codegen/src/api/calls.rs

@@ -116,7 +116,7 @@ pub fn generate_calls(
             where
                 T: ::subxt::Config,
                 X: ::subxt::SignedExtra<T>,
-                A: ::subxt::AccountData<T>,
+                A: ::subxt::AccountData,
             {
                 pub fn new(client: &'a ::subxt::Client<T>) -> Self {
                     Self { client, marker: ::core::marker::PhantomData }

codegen/src/api/mod.rs

@@ -14,6 +14,23 @@
 // You should have received a copy of the GNU General Public License
 // along with subxt.  If not, see <http://www.gnu.org/licenses/>.
 
+//! Generate code for submitting extrinsics and query storage of a Substrate runtime.
+//!
+//! ## Note
+//!
+//! By default the codegen will search for the `System` pallet's `Account` storage item, which is
+//! the conventional location where an account's index (aka nonce) is stored.
+//!
+//! If this `System::Account` storage item is discovered, then it is assumed that:
+//!
+//!   1. The type of the storage item is a `struct` (aka a composite type)
+//!   2. There exists a field called `nonce` which contains the account index.
+//!
+//! These assumptions are based on the fact that the `frame_system::AccountInfo` type is the default
+//! configured type, and that the vast majority of chain configurations will use this.
+//!
+//! If either of these conditions are not satisfied, the codegen will fail.
+
 mod calls;
 mod constants;
 mod errors;
@@ -32,8 +49,10 @@ use crate::{
 use codec::Decode;
 use frame_metadata::{
     v14::RuntimeMetadataV14,
+    PalletMetadata,
     RuntimeMetadata,
     RuntimeMetadataPrefixed,
+    StorageEntryType,
 };
 use heck::SnakeCase as _;
 use proc_macro2::TokenStream as TokenStream2;
@@ -42,6 +61,7 @@ use quote::{
     format_ident,
     quote,
 };
+use scale_info::form::PortableForm;
 use std::{
     collections::HashMap,
     fs,
@@ -242,6 +262,16 @@ impl RuntimeGenerator {
         let error_type = error_details.type_def;
         let error_fn = error_details.dispatch_error_impl_fn;
 
+        let default_account_data_ident = format_ident!("DefaultAccountData");
+        let default_account_data_impl = generate_default_account_data_impl(
+            &pallets_with_mod_names,
+            &default_account_data_ident,
+            &type_gen,
+        );
+        let type_parameter_default_impl = default_account_data_impl
+            .as_ref()
+            .map(|_| quote!( = #default_account_data_ident ));
+
         quote! {
             #[allow(dead_code, unused_imports, non_camel_case_types)]
             pub mod #mod_ident {
@@ -249,10 +279,6 @@ impl RuntimeGenerator {
                 #( #modules )*
                 #types_mod
 
-                /// The default storage entry from which to fetch an account nonce, required for
-                /// constructing a transaction.
-                pub type DefaultAccountData = self::system::storage::Account;
-
                 /// The default error type returned when there is a runtime issue.
                 pub type DispatchError = self::runtime_types::sp_runtime::DispatchError;
 
@@ -262,34 +288,29 @@ impl RuntimeGenerator {
                     #error_fn
                 }
 
-                impl ::subxt::AccountData<::subxt::DefaultConfig> for DefaultAccountData {
-                    fn nonce(result: &<Self as ::subxt::StorageEntry>::Value) -> <::subxt::DefaultConfig as ::subxt::Config>::Index {
-                        result.nonce
-                    }
-                    fn storage_entry(account_id: <::subxt::DefaultConfig as ::subxt::Config>::AccountId) -> Self {
-                        Self(account_id)
-                    }
-                }
+                #default_account_data_impl
 
-                pub struct RuntimeApi<T: ::subxt::Config, X> {
+                pub struct RuntimeApi<T: ::subxt::Config, X, A #type_parameter_default_impl> {
                     pub client: ::subxt::Client<T>,
-                    marker: ::core::marker::PhantomData<X>,
+                    marker: ::core::marker::PhantomData<(X, A)>,
                 }
 
-                impl<T, X> ::core::convert::From<::subxt::Client<T>> for RuntimeApi<T, X>
+                impl<T, X, A> ::core::convert::From<::subxt::Client<T>> for RuntimeApi<T, X, A>
                 where
                     T: ::subxt::Config,
                     X: ::subxt::SignedExtra<T>,
+                    A: ::subxt::AccountData,
                 {
                     fn from(client: ::subxt::Client<T>) -> Self {
                         Self { client, marker: ::core::marker::PhantomData }
                     }
                 }
 
-                impl<'a, T, X> RuntimeApi<T, X>
+                impl<'a, T, X, A> RuntimeApi<T, X, A>
                 where
                     T: ::subxt::Config,
                     X: ::subxt::SignedExtra<T>,
+                    A: ::subxt::AccountData,
                 {
                     pub fn constants(&'a self) -> ConstantsApi {
                         ConstantsApi
@@ -299,7 +320,7 @@ impl RuntimeGenerator {
                         StorageApi { client: &self.client }
                     }
 
-                    pub fn tx(&'a self) -> TransactionApi<'a, T, X, DefaultAccountData> {
+                    pub fn tx(&'a self) -> TransactionApi<'a, T, X, A> {
                         TransactionApi { client: &self.client, marker: ::core::marker::PhantomData }
                     }
                 }
@@ -339,7 +360,7 @@ impl RuntimeGenerator {
                 where
                     T: ::subxt::Config,
                     X: ::subxt::SignedExtra<T>,
-                    A: ::subxt::AccountData<T>,
+                    A: ::subxt::AccountData,
                 {
                     #(
                         pub fn #pallets_with_calls(&self) -> #pallets_with_calls::calls::TransactionApi<'a, T, X, A> {
@@ -352,6 +373,72 @@ impl RuntimeGenerator {
     }
 }
 
+/// Most chains require a valid account nonce as part of the extrinsic, so the default behaviour of
+/// the client is to fetch the nonce for the current account.
+///
+/// The account index (aka nonce) is commonly stored in the `System` pallet's `Account` storage item.
+/// This function attempts to find that storage item, and if it is present will implement the
+/// `subxt::AccountData` trait for it. This allows the client to construct the appropriate
+/// storage key from the account id, and then retrieve the `nonce` from the resulting storage item.
+fn generate_default_account_data_impl(
+    pallets_with_mod_names: &[(&PalletMetadata<PortableForm>, syn::Ident)],
+    default_impl_name: &syn::Ident,
+    type_gen: &TypeGenerator,
+) -> Option<TokenStream2> {
+    let storage = pallets_with_mod_names
+        .iter()
+        .find(|(pallet, _)| pallet.name == "System")
+        .and_then(|(pallet, _)| pallet.storage.as_ref())?;
+    let storage_entry = storage
+        .entries
+        .iter()
+        .find(|entry| entry.name == "Account")?;
+
+    // resolve the concrete types for `AccountId` (to build the key) and `Index` to extract the
+    // account index (nonce) value from the result.
+    let (account_id_ty, account_nonce_ty) =
+        if let StorageEntryType::Map { key, value, .. } = &storage_entry.ty {
+            let account_id_ty = type_gen.resolve_type_path(key.id(), &[]);
+            let account_data_ty = type_gen.resolve_type(value.id());
+            let nonce_field = if let scale_info::TypeDef::Composite(composite) =
+                account_data_ty.type_def()
+            {
+                composite
+                    .fields()
+                    .iter()
+                    .find(|f| f.name() == Some(&"nonce".to_string()))?
+            } else {
+                abort_call_site!("Expected a `nonce` field in the account info struct")
+            };
+            let account_nonce_ty = type_gen.resolve_type_path(nonce_field.ty().id(), &[]);
+            (account_id_ty, account_nonce_ty)
+        } else {
+            abort_call_site!("System::Account should be a `StorageEntryType::Map`")
+        };
+
+    // this path to the storage entry depends on storage codegen.
+    let storage_entry_path = quote!(self::system::storage::Account);
+
+    Some(quote! {
+        /// The default storage entry from which to fetch an account nonce, required for
+        /// constructing a transaction.
+        pub enum #default_impl_name {}
+
+        impl ::subxt::AccountData for #default_impl_name {
+            type StorageEntry = #storage_entry_path;
+            type AccountId = #account_id_ty;
+            type Index = #account_nonce_ty;
+
+            fn nonce(result: &<Self::StorageEntry as ::subxt::StorageEntry>::Value) -> Self::Index {
+                result.nonce
+            }
+            fn storage_entry(account_id: Self::AccountId) -> Self::StorageEntry {
+                #storage_entry_path(account_id)
+            }
+        }
+    })
+}
+
 pub fn generate_structs_from_variants<'a, F>(
     type_gen: &'a TypeGenerator,
     type_id: u32,